Transmission Having Planetary Gear Drive With Variable Speed Reduction

ABSTRACT

A transmission for transferring torque from a prime mover includes a first input shaft adapted to be driven by the prime mover, a second input shaft and an output shaft. A compound planetary gearset includes a sun gear driven by the first input shaft, first pinion gears being driven by the sun gear, a ring gear fixed for rotation with the second input shaft and being meshed with second pinion gears, and a carrier driving the output shaft. A reaction motor drives the second input shaft. A controller controls the reaction motor to vary the speed of the second input shaft and define a gear ratio between the first input shaft and the output shaft based on the second input shaft speed.

FIELD

The present disclosure relates to power transmission devices. Moreparticularly, a transmission for transferring torque at a variable speedreduction ratio includes a planetary gear drive driven by two sources ofpower.

BACKGROUND

Geared transmissions typically function to change the rotational speedof a prime mover output shaft and an input shaft of a desired workoutput. In a vehicle, the prime mover may include a diesel or gasolineinternal combustion engine. It should be noted that there are many moreapplications than automobiles and trucks. Locomotives are equipped withtransmissions between their engines and their wheels. Bicycles andmotorcycles also include a transmission. Speed-increasing transmissionsallow large, slow-moving blades of a windmill to generate power muchcloser to a desired AC frequency. Other industrial applications exist.In each case, the motor and transmission act together to provide powerat a desired speed and torque to do useful work. Geared transmissionshave also been used in combination with electric motors acting as theprime mover.

Multiple speed transmissions have been coupled to high torque primemovers that typically operate within a narrow speed range, most notablystructured as large displacement diesel engines of tractor trailers.Electric motors have a much wider speed range in which they operateeffectively. However, the motor operates most efficiently at a singlespeed. Known multiple speed transmissions attempt to maintain an optimumoperating speed and torque of the

prime mover output shaft, but only approximate this condition due to thediscrete gear ratios provided. Accordingly, a need for a simplifiedvariable speed ratio power transmission device exists.

Many existing transmissions incorporate planetary gearsets within thetorque path. A traditional planetary gear drive has three majorcomponents: a sun gear, an annulus ring gear and a planet carrier. Whenone of those components is connected to the prime mover, another is usedas the output and the third component is not allowed to rotate. Theinput and output may rotate at different speeds, and may also rotate inopposite directions, with the ratio of input to output speeds being afixed value. When the previously fixed third component is connected to asecond input and forced to rotate, the transmission will have acontinuously varying speed ratio dependent on the speeds of both theprime mover and this new second input. One example of such a planetarygear drive is made by Toyota. While planetary gearsets have beensuccessfully used in vehicle power transmissions in the past, a needexists for a planetary drive and control system for optimizing the geardrive's efficiency and power density.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A transmission for transferring torque from a prime mover includes afirst input shaft adapted to be driven by the prime mover, a secondinput shaft and an output shaft. A compound planetary gearset includes asun gear driven by the first input shaft, first pinion gears beingdriven by the sun gear, a ring gear fixed for rotation with the secondinput shaft and being meshed with second pinion gears, and a carrierdriving the output shaft. A reaction motor drives the second inputshaft. A controller controls the reaction motor to vary the speed of thesecond input shaft and define a gear ratio between the first input shaftand the output shaft based on the second input shaft speed.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic depicting an exemplary vehicle equipped with atransmission constructed in accordance with the teachings of the presentdisclosure;

FIG. 2 is a schematic representation of a transmission having a simpleplanetary gearset;

FIG. 3 is a graph depicting sun speed to carrier speed ratio versus ringspeed to sun speed ratio for a number of fixed ring ratios of a simpleplanetary gearset;

FIG. 4 depicts relative diameters of sun, planet and annulus ring gearsfor a planetary gearset having a fixed ring ratio of 9.706.

FIG. 5 is a schematic depicting a transmission equipped with a compoundplanetary gearset;

FIG. 6 is a graph depicting sun speed to carrier speed ratio versus ringspeed to sun speed ratio for a number of compound planetary gearsets;

FIG. 7 is a schematic of an alternate transmission including a simpleplanetary gearset and an offset motor and speed reduction unit;

FIG. 8 is a schematic depicting another transmission having a compoundplanetary gearset driven by an offset reaction motor and speed reductionunit;

FIG. 9 is a schematic of another transmission including two simpleplanetary gearsets;

FIG. 10 is a schematic of another transmission equipped with a compoundplanetary gearset and a simple planetary reduction gearset;

FIGS. 11 and 12 depict alternate transmissions including worm and wormwheel drives; and

FIGS. 13 and 14 depict alternative transmissions includingconcentrically arranged worm drive mechanisms.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The present disclosure is directed to a transmission that can beadaptively controlled to transfer torque between a first rotary memberand a second rotary member. The transmission finds particularapplication in motor vehicle drivelines such as, for example, acontinuously variable torque transfer mechanism. Thus, while thetransmission of the present disclosure is hereinafter described inassociation with particular arrangements for use in specific drivelineapplications, it will be understood that the arrangements shown anddescribed are merely intended to illustrate embodiments of the presentdisclosure.

With particular reference to FIG. 1 of the drawings, a drivetrain 10 foran all-wheel drive vehicle is shown. Drivetrain 10 includes a driveline12 and a powertrain 16 for delivering rotary tractive power (i.e., drivetorque) to the driveline. In the particular arrangement shown, driveline12 is the rear driveline. Powertrain 16 is shown to include an engine 18and a transmission 20. A pair of front wheels 24L and 24R are notdriven. Driveline 12 includes a propshaft 30 driven by transmission 20and a rear axle assembly 32 for transferring drive torque from engine 18to a rear differential 34. A pair of rear axleshafts 38L and 38Rinterconnect rear differential 34 to corresponding rear wheels 36L and36R.

As shown in FIGS. 1 and 2, transmission 20 includes a planetary gearset40 and a reaction motor 42. Drivetrain 10 is shown to further includevehicle sensors 44 for detecting certain dynamic and operationalcharacteristics of the motor vehicle and a controller 45 for controllingactuation of reaction motor 42 in response to input signals from vehiclesensors 44.

Planetary gearset 40 includes a sun gear 46 fixed for rotation with anoutput shaft 48 of engine 18. An annulus ring gear 50 is fixed forrotation with an output shaft 52 of reaction motor 42. Planetary gearset40 also includes a carrier 54 rotatably supporting a plurality of piniongears 56 that are each in constant meshed engagement with annulus ringgear 50 and sun gear 46. An output shaft 58 is fixed for rotation withcarrier 54. The remainder of this disclosure discusses how the sun gearspeed ω_(S) to carrier speed ω_(C) ratio is a function of an annulusring gear speed ω_(R) to sun speed ω_(S) in simple and compoundplanetary gearsets and how the asymptotic nature of this speed ratio maybe exploited to improve the gear drive's efficiency and power density.

If a positive direction of annulus ring rotation is defined to be in thesame direction as that of the sun gear and carrier assembly, it can beshown that in the general case, the ratio of sun to carrier speeds isgiven by:

$\begin{matrix}{\frac{\omega_{S}}{\omega_{C}} = {\frac{z_{S} + z_{R}}{z_{S}}\left\lbrack {1 - \left( \frac{\omega_{R}z_{R}}{{\omega_{S}z_{S}} + {\omega_{R}z_{R}}} \right)} \right\rbrack}} & (1)\end{matrix}$

where ω_(S), ω_(C), and ω_(R) are the sun, carrier and annulus ringangular velocities and z_(R) and z_(S) are the number of teeth in theannulus ring and sun gears, respectively. Note that if ω_(R)=0, equation(1) simplifies to the familiar relationship between sun and carrierspeeds for a fixed annulus ring.We define the ratio of ring speed to sun speed as

$\begin{matrix}{\Omega = \frac{\omega_{R}}{\omega_{S}}} & (2)\end{matrix}$

Equation (1) may then be rewritten as

$\begin{matrix}{\frac{\omega_{S}}{\omega_{C}} = \frac{z_{R} + z_{S}}{z_{S} + {\Omega \cdot z_{R}}}} & (3)\end{matrix}$

It can be noted that there will be a value of Ω for which ω_(S)/ω_(C)will become asymptotic. FIG. 1 shows equation (3) plotted against thering to sun speed ratio for different numbers of ring and sun gearteeth. Each curve is labeled with its carrier to sun fixed ring ratio(FRR). Table 1 lists the number of teeth in the sun, planets and ring ofeach planetary combination, as well as each tooth combination's FRR. Thecombinations of sun, planet and ring gear tooth numbers were selected tospan the practical limits of geometry limitations.

FIG. 3 plots the speed ratio ω_(S)/ω_(C) against Ω for various FRRvalues listed in Table 1 and shows that the vertical asymptote increasesfrom Ω=−0.650 to −0.115 as the FRR increases. More importantly, themagnitude of the ω_(S)/ω_(C) slope as the curve crosses the ordinateaxis Ω=0 increases as well. As the magnitude of the ω_(S)/ω_(C) slopeincreases, the annulus ring speed required to effect a change in thespeed ratio ω_(S)/ω_(C) decreases dramatically. The annulus ring gear50, however, is the largest of all component gears in the planetarygearset 40. As such, a relatively large torque may need to be reacted byreaction motor 42. The torque necessary to supply a sufficient reactionto pinion gears 56 may be quite large as well.

The sensitivity of the speed ratio to its fixed ring ratio is quantifiedby defining the ratio of the highest to lowest speed ratios as Δ for anarbitrary value of Ω selected as +/−10% of the sun's speed, as well asthe value of Ω for the vertical asymptote. Table 1 presents this data.

TABLE 1 Simple Planetary Tooth Combinations Numbers of Teeth Fixed RingRatio Spread Vertical Sun Planets Ring Speed Ratio Δ =(ω_(S)/ω_(C))_(MAX)/(ω_(S)/ω_(C))_(MIN) Asypmptote Z_(S) Z_(P) Z_(R)(Z_(S) + Z_(R))/Z_(S) −0.1 < Ω < 0.1 Ω = ω_(R)/ω_(S) 17 65 148 9.70614.455 −0.115 20 62 145 8.250 6.273 −0.138 23 59 142 7.174 4.227 −0.16228 54 137 5.893 2.916 −0.204 34 48 131 4.853 2.254 −0.260 41 41 1244.024 1.867 −0.331 52 30 113 3.173 1.555 −0.460 65 17 100 2.538 1.364−0.650

Table 1 and FIG. 3 illustrate that a large fixed ring ratio (FRR) isnecessary to have the desirable feature of ω_(S)/ω_(C) speed ratiosensitivity. Design constraints may exist where such a large FRR is notpractical. FIG. 4 shows the relative diameters of the sun, planets andannulus ring of the 9.706 FRR planetary. The relatively small sun sizewill limit the strength of the shaft on which the sun gear is fixed.Furthermore, just as there is a minimum practical FRR, below which theplanet pinions are too small to be supported with rolling elementbearings, there is a maximum FRR, above which the tips of the planetpinions will interfere.

FIG. 5 depicts an alternative transmission 20 a having a compoundplanetary gearset 40 a in lieu of simple planetary gearset 40.Alternative transmission 20 a is substantially similar to transmission20. Accordingly, like elements will be identified with referencenumerals including an “a” suffix. Planetary gearset 40 a differs fromsimple planetary gearset 40 in that compound pinion gears 60 replacepinion gears 56. Each compound pinion gear 60 includes a first piniongear 62 in meshed engagement with sun gear 46 a as well as a reduceddiameter second pinion gear 64 in constant meshed engagement withannulus ring gear 50 a. First pinion gears 62 have a predeterminednumber of teeth, module, pressure angle and helix angle based on themesh with sun gear 46 a. Second pinion gears 64 have a reduced number ofteeth, a different module, pressure angle and helix angle for the gearmeshes with annulus ring gear 50 a. The compound planetary gearsetprovides a minimized inner and outer radial packaging. Furthermore, thecompound planetary gearset provides a greater reduction gear ratio. Itshould be appreciated that first pinion gears 62 and second pinion gears64 are aligned in pairs to rotate on common pinion centers.

To operate on the same pinion centers, the module, helix angle andnumber of teeth must satisfy this constraint:

$\begin{matrix}{\frac{m_{R}\cos \; \beta_{S}}{m_{s}\cos \; \beta_{R}} = \frac{z_{S} + z_{PS}}{z_{R} - z_{PR}}} & (4)\end{matrix}$

where m_(R) and m_(S) are the normal modules of the ring and sun meshes,respectively. The planet pinions z_(PS) and z_(PR) mesh with the sun andannulus, respectively. In addition to the geometry constraint ofequation (4), each of the compound planet pinions independent meshesmust have the same torque, but because each torque will act at differentpitch geometries, the tooth loads may differ significantly and requirelargely different modules as a result.

If the design of a compound planetary gear set is modified to allow foran annulus gear that may move at a controlled angular speed while stillproviding the necessary reaction torque for the planet pinions, asimilar asymptotic behavior to that seen in FIG. 3 exists. With the samereasoning used to develop equations (1) and (2), it can be shown thatthe speed ratio ω_(S)/ω_(C) of a compound planetary gear set, in whichthe annulus gear is allowed to rotate is given by:

$\begin{matrix}{\frac{\omega_{S}}{\omega_{C}} = \frac{{z_{R} \cdot z_{PS}} + {z_{S} \cdot z_{PR}}}{{z_{S} \cdot z_{PR}} + {\Omega \cdot z_{R} \cdot z_{PS}}}} & (5)\end{matrix}$

As with equations (1) and (2), equation (5) reduces to the familiarspeed relationship for a fixed annulus ring when Ω=0. Since a compoundplanetary gear set is capable for a larger speed ratio ω_(S)/ω_(C), thebenefits of the asymptotic nature of equation (5) can be more fullyexploited. FIG. 6 shows the sun-carrier speed ratios again plottedagainst ring-sun speed ratios for different fixed ring ratios.

TABLE 2 Compound Planetary Tooth Combinations Numbers of Teeth PlanetsPlanets Fixed Ring Ratio Spread Sun (Sun) (Ring) Ring Speed Ratio Δ =(ω_(S)/ω_(C))_(MAX)/(ω_(S)/ω_(C))_(MIN) Z_(S) Z_(PS) Z_(PR) Z_(R)(Z_(S)Z_(PR) + Z_(R)Z_(PS))/(Z_(S)Z_(PR)) −0.03 < Ω < 0.03 19 79 17 11529.127 11.805 22 79 17 115 25.291 6.373 23 76 17 98 20.049 3.667 29 6817 100 14.793 2.412 35 64 19 94 10.047 1.745 37 50 23 107 7.287 1.465 4746 23 95 5.043 1.276

As was done for simple planetary gear drives, tooth combinations shownin Table 2 were selected to attempt to span the practical FRR limits. AFRR less than 5.043 would most likely not justify the additionalcomplexity and expense of a compound planetary over a simple planetaryand a FRR larger than 30 may not be practical, as can be seen from FIG.6. It is also noted that in comparing FIGS. 3 and 6, it can be seen fora given FRR a compound planetary will have a larger asymptote value thana simple planetary.

FIG. 7 depicts an alternate transmission 20 b and is constructedsubstantially similarly to transmission 20. Similar elements will beidentified with like reference numerals including a “b” suffix. Areaction motor 42 b includes an output shaft 52 b that extends offsetand parallel to an axis of rotation of output shaft 58 b. Reaction motor42 b drives a reduction gearset 72 to rotate ring gear 50 b. Reductiongearset 72 includes a first gear 76 fixed for rotation with output shaft52 b. A second gear 78 is in constant meshed engagement with first gear76 and is fixed for rotation with a concentric shaft 80. Annulus ringgear 50 b is also fixed for rotation with concentric shaft 80.

FIG. 8 depicts an alternate transmission identified at reference numeral20 c. Transmission 20 c includes the offset motor and speed reductionunit arrangement shown in FIG. 7 being used in conjunction with thecompound planetary gearset first described at FIG. 5. Accordingly,similar elements will be identified with like reference numeralsincluding a “c” suffix. In operation, reaction motor 42 c drives firstgear 76 c and second gear 78 c to rotate annulus ring gear 50 c and varythe output ratio provided to output shaft 58 c.

FIG. 9 depicts another alternate transmission identified at referencenumeral 20 d. Transmission 20 d is substantially similar to transmission20 with the addition of a planetary reduction gearset 90. Similarelements will be identified with like reference numerals having a “d”suffix. Planetary gearset 90 includes a sun gear 92 fixed for rotationwith reaction motor output shaft 52 d. Reaction motor output shaft 52 dis concentrically aligned with and circumscribes output shaft 58 d. Aring gear 94 is restricted from rotation. A plurality of pinion gears 96are supported for rotation on a carrier 98. Pinion gears 96 are eachmeshed with sun gear 92 and ring gear 94. Carrier 98 is fixed forrotation with a concentric shaft 100. Annulus ring gear 50 d is alsofixed for rotation with concentric shaft 100.

FIG. 10 depicts another alternate transmission 20 e that incorporatesthe planetary reduction gearset of FIG. 9 and mates it with the compoundplanetary gear arrangement shown in FIG. 5. Similar elements will beidentified with like reference numerals having a “e” suffix. Reactionmotor 42 e includes an output shaft 52 e transferring torque toplanetary reduction unit 90 e. Carrier 98 e is fixed for rotation withconcentric shaft 100 e and annulus ring gear 50 e.

FIGS. 11 and 12 depict alternate transmissions 20 f and 20 g,respectively. Each of transmissions 20 f, 20 g include a worm drive 110including a reaction motor 42 f, 42 g, driving a worm gear 112 along anaxis of rotation that extends substantially perpendicular to an axis ofrotation of output shaft 58 f, 58 g. Worm gear 112 is in constant meshedengagement with a worm wheel 114. Worm wheel 114 is fixed for rotationwith a concentric shaft 116. In FIG. 11, concentric shaft 116 is fixedfor rotation with annulus ring gear 50 f. In similar fashion, concentricshaft 116 of FIG. 12 is fixed for rotation with annulus ring gear 50 g.

FIGS. 13 and 14 also depict alternative transmissions identified atreference numerals 20 h and 20 i, respectively. FIGS. 13 and 14 aresubstantially similar to FIGS. 11 and 12 except that worm wheels 114 h,114 i concentrically surround annular ring gears 50 h and 50 i.

Furthermore, the foregoing discussion discloses and describes merelyexemplary embodiments of the present disclosure. One skilled in the artwill readily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationsmay be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

1. A transmission for transferring torque from a prime mover, thetransmission comprising: a first input shaft adapted to be driven by theprime mover; a second input shaft; an output shaft; a compound planetarygearset including a sun gear being driven by the first input shaft,first pinion gears being driven by the sun gear, a ring gear fixed forrotation with the second input shaft and being meshed with second piniongears, and a carrier driving the output shaft; a reaction motor drivingthe second input shaft; and a controller for controlling the reactionmotor to vary the speed of the second input shaft and define a gearratio between the first input shaft and the output shaft based on thesecond input shaft speed.
 2. The transmission of claim 1 wherein thereaction motor rotates the second input shaft in an opposite directionas the first input shaft.
 3. The transmission of claim 1 wherein thetransmission is operable in a neutral mode where the output shaft is notrotating when the first and second input shafts are rotating.
 4. Thetransmission of claim 1 wherein a fixed ring ratio of the compoundplanetary gearset ranges between 5 and
 25. 5. The transmission of claim1 wherein a vertical asymptote of a ratio of sun gear speed to carrierspeed versus a ratio of ring gear speed to sun gear speed ranges between0.00 and −0.25.
 6. The transmission of claim 1 wherein the second inputshaft is concentrically arranged with the output shaft.
 7. Thetransmission of claim 1 wherein the second input shaft extendssubstantially parallel to and offset from the output shaft.
 8. Thetransmission of claim 1 further including a reduction gearset driven bythe second input shaft and driving the ring gear.
 9. The transmission ofclaim 8 wherein the reduction gearset includes a drive gear meshed witha driven gear rotating about offset axes.
 10. The transmission of claim8 wherein the reduction gearset includes a worm gear fixed for rotationwith the second input shaft and a worm wheel driving the ring gear. 11.The transmission of claim 8 wherein the reduction gearset includes aplanetary gearset and the second input shaft, the first input shaft andthe output shaft rotate about a common axis.
 12. A method of providingvariable speed reduction through a transmission having a planetary geardrive, the method comprising: selecting a sun gear, first and secondpinion gears, a carrier and a ring gear of a planetary gearset to definea fixed ring ratio ranging between 10-25; rotatably supporting the firstand second pinion gears on the carrier; positioning the first piniongears in meshed engagement with the sun gear; positioning the secondpinion gears in meshed engagement with the ring gear; fixing a firstinput shaft for rotation with the sun gear; fixing the carrier forrotation with an output shaft; fixing a second input shaft to the ringgear; driving the first input shaft by a prime mover; and driving thesecond input shaft with the reaction motor wherein a gear ratio betweenthe first input shaft and the output shaft varies based on the secondinput shaft speed.
 13. The method of claim 12 further includingdetermining a vertical asymptote of a ratio of sun gear speed to carrierspeed versus a ratio of ring gear speed to sun gear speed and minimizinga difference between the vertical asymptote and
 0. 14. The method ofclaim 13 further including controlling the reaction motor to rotate thesecond input shaft in an opposite direction as the first input shaft.15. The method of claim 14 further including operating the transmissionin a neutral mode by controlling the speed of the second input shaftsuch that the output shaft does not rotate.
 16. The method of claim 15further including concentrically arranging the second input shaft withthe output shaft.
 17. The method of claim 16 further including driving areduction gearset with the reaction motor and providing an output fromthe reduction gearset to the ring gear.